This invention generally relates to a method of detecting a failure in a roller. More particularly, the invention pertains to a method for detecting a roller failure at a roller in a continuous casting machine.
A continuous casting machine produces steel material from molten steel. This steel material can, for example, be used as the starting material in rolling processes for producing sheet metal. The sheet metal can be used, for instance, in vehicles.
In the continuous casting machine, molten steel flows from a ladle and down in a tundish from which it is further transported down into a mold. In the mold, which is water-cooled, the slab of continuous cast material begins to form a solid shell. The slab is then continuously transported along a curved track by a large number of rollers arranged in segments which continue to shape and cool the slab to the final thickness of the steel material. At the end of the track, the material is cut into suitable pieces.
The rollers of the continuous casting machine are mounted with their axes substantially perpendicular to the longitudinal extension of the curved track. To be able to lead and support the slab of continuous cast material, the rollers are arranged in pairs, with each comprising an upper roller and a lower roller.
Further, the rollers are supported in bearings at each end of the rollers. Due to the length of the rollers, and thus their weight, the rollers are generally split into at least two roller portions. The roller portions are either independently supported in bearings or non-rotatably provided on a common shaft, with the shaft being supported in bearings.
A serious problem that can occur during continuous casting is that cracks can arise in the cast material due to roller failure. Such roller failures can mainly be caused by one or several bearing failures and/or mounting failures, both of which lead to one or several rollers no longer being aligned with the imagined extension of the track of rollers. A further cause can be excessive wear of one roller compared to the other rollers.
Generally speaking, a bearing and/or bearing housing failure refers to a failure that occurs during operation of the continuous casting machine and is often caused by loads exceeding permitted loads or wear in the bearings caused by, for example, dirt. A bearing and/or bearing housing failure is called a xe2x80x9ccollapsexe2x80x9d. The result of such a collapse is that the roller supported in the collapsed bearing and/or bearing housing cannot support the slab as much as before due to the fact that the position of the roller changes in direction substantially away from the slab. That is, the collapsed roller is no longer aligned with the imagined extension of the track of rollers and therefore the contact with the slab decreases. In those cases where the liquid core of the slab is very small, i.e., in the section of the machine where the slab is more or less entirely solidified, the roller loses all of its contact with the slab.
As used herein, a mounting failure refers to an initial misalignment of one or several rollers and/or segments compared to the imagined extension of the track of rollers. Usually, when setting up a machine, a number of rollers are first mounted together to form track segments. These segments are later lifted into the machine. This procedure saves assembly time because the frame of the machine and the track segments can be assembled simultaneously. Also, track segments are often assembled in advance and are kept standing by in case any segment in the machine needs to be rapidly exchanged due to failure.
When mounting together the rollers to form segments, the rollers within a segment are aligned to each other with conventional measuring equipment such as, for example, a ruler. However, when these segments are later mounted in the continuous casting machine, it is very likely that the alignment between the rollers in the segments might become more or less destroyed because of the size, weight and ungainliness of the segments. For the same reasons, it is also very likely that entire segments in the machine will not be correctly aligned with the imagined extension of the track of rollers, that is with segments that are correctly positioned in the track.
Because the size of the rollers and the segments in a continuous casting machine is very large and the divergence between the normal position of the roller and/or segment and the misaligned position is relatively small, it is usually very difficult to distinguish a misaligned roller and/or segment from the rest of the rollers and/or segments. This is unfortunate as the cracks arising from these misalignments (i.e., from less support or the sudden lack of material) can cause relatively great damage to the material.
These cracks can be either internal cracks or surface cracks, both of which lead to decreased quality as a material having cracks will be almost impossible to roll. Surface cracks can be treated by costly treatment after the casting process. One way of treating the surface cracks is to weld them. Another way to treat the surface cracks is to grind off the surface layer of the material. Both alternatives are expensive and cannot give a perfect result. The steel thus has to be classified in a lower quality class. Material with internal cracks cannot be treated and must be discarded.
A need thus exists for a method of detecting roller failures, for example bearing or mounting failures, at rollers and or segments in a continuous casting machine.
A method for detecting roller failures, e.g. bearing or mounting failures, at rollers and or segments in a continuous casting machine involves determining a radial target load value exerted by the material on a roller, measuring the actual load value on at least each second roller in the row of rollers, comparing the measured actual load value with the determined target load value, detecting a possible divergence between the actual load value and the target load value, and establishing the presence of a roller failure at such a divergence.
Another aspect involves a method for detecting a roller failure in a continuous casting machine that is comprised of a row of rollers supported in bearings and arranged one after another for transporting material produced in the machine. The method includes measuring an actual radial load value exerted by the material being transported on one of the rollers, comparing the measured actual radial load value with a target radial load value, detecting a divergence between the measured actual radial load value and the target radial load value, and determining that a failure of the roller exists upon detecting a divergence between the actual radial load value and the target radial load value.